“It is made of unslaked lime and beaten brick most finely powdered and sifted, cotton wool very thinly pulled and strewed on, and then all slaked with linseed oil and mixed together: then they use it whilst it is fresh made, otherwise it hardens immediately.”[349] Such a cement must have had the hardening qualities of gesso; the oil cements or mastics used in England some fifty years ago were closely allied in their composition. Modern mortar has lost much by our neglecting the tradition of using crushed brick. Eastern builders spared neither labour nor time in preparing and testing their materials. Tavernier tells us the waterproof terraces of the Persian houses were formed of “a layer of lime beaten for eight days, which became hard like marble.” The materials used in Byzantine building were tested by long exposure, slaked lime was sealed up in pits for one or two years; and stones, bricks, and tiles they had found should not be used new, for, as Vitruvius says, “the only way of ascertaining their goodness is to try them through a summer and winter.” CHAPTER XI MARBLE MASONRY § 1. BUILDING PROCEDURE. The method and sequence of the building operations as followed by the Byzantines seem to have been very much as follows. After the form of the building had been more or less decided, the first thing necessary was to collect marble monolithic shafts. At S. Sophia the eight verde-antique shafts match one another very closely; they are all of one length, and vary from 7½ to 8 diameters in proportion. The four pairs of porphyry shafts in the exedras differ much more; and, as we have remarked, those in the western exedras seem to be made up of separate drums. The proportions of these vary from less than 7 diameters on one side to 8½ on the other. The great monoliths are the largest known, and of nearly normal classic proportion, so we can readily see that it was necessary to have a certain knowledge where such marbles might be quarried or otherwise obtained, before even the foundations were prepared, for the columns decided the heights and points of support of the building. These once assured, the body of the structure was proceeded with as a brickwork shell without further dependence on the masons, who were only required to prepare bases and capitals, and then the cornices; everything else was completed as a brick “carcase.” At S. Sophia the main square piers are in fact stone, but this was only for strength, not because they were to be seen finally, any more than the rough brick.